The broad objective of the proposed research is the synthesis, characterization, and study of the reactivity of a broad class of metal complexes of cobalt and iron, in their common oxidation states, which may serve as models for their naturally occurring biological counterparts. The proposed ligand systems have been designed to contain a variety of electronic and structural features (in particular, steric constraints) that will encompass those of the naturally occurring heme and corrinoid environments. Three areas will be focused upon: 1) The interaction of oxygen and carbon monoxide with iron(II) complexes of specially designed polycyclic ligands will be studied with particular emphasis on the isolation of dioxygen complexes and the characterization of iron(II) complexes containing angular Fe-C triple bond O bonds. 2) New cobalt(III)-alkyl complexes containing strained Co-C bonds will be synthesized and their reactivity will be compared with those of the unstrained counterparts. 3) The synthesis, characterization, and study of co-facial binuclear metal complexes in which the metal atoms are intentially positioned forcing them to simultaneously interact with substrates that approach their axial coordination sites will be initiated. The electronic and molecular structures of all new complexes will be examined with electronic and nuclear magnetic resonance spectroscopy (primarily 1H and 13C) and selected compounds will be subjected to full scale structural determination via x-ray crystallography.